The Influence of the Plant Growth-regulator, 2-Methyl-4-Chlorophenoxyacetic Acid, on the Metabolism of Carbohydrate, Nitrogen and Minerals in Solanum lycopersicum (Tomato)

The effects of the foliar application of phytocidal concentrationsof 2-methyl-4-chlorophenoxyacetic acid (MCPA) on change in totaldry weight, and in ‘available carbohydrate’ (starch,‘total’ and ‘reducing’ sugars), totalnitrogen, phosphorus, potassium, calcium, and magnesium of ‘tops’and roots of tomato plants have been followed over a periodof 14 days following spraying. There were two main treatments—‘nutrient’(nutrient supply to roots continued after spraying) and ‘water’(distilled water only supplied to roots after spraying) and‘water’ (distilled water only supplied to rootsafter spraying)—the sub-treatments consisting of ‘MCPA’versus ‘no-MCPA’ for each of the main treatments.Twelve different times of sampling were used. In analysing the present data, the quantity ‘residualdry weight’ (total dry weight less ‘available carbohydrate’),which was originally introduced by Mason and Maskell as a basisof reference for analyses of plant organs in short-period experimentsnot involving appreciable growth, has been used as an estimateof the permanent structure of plant growth. This new use ofthe ‘residual dry weight’ basis has brought outimportant features which were obscured when the data were leftin their primary form (as percentages of total dry weight oramounts per plant). Growth, as measured by increase in ‘residual dry weight’,was greatly inhibited by 2-methyl-4-chlorophenoxyacetic acidshortly after spraying, in both the presence and the absenceof nutrient. In the presence of 2-methyl-4-chlorophenoxyacetic acid, netassimilation rate (estimated as rate of increase in total dryweight per gram ‘residual dry weight’ of the ‘tops’)was greatly diminished while uptake of total nitrogen and ofP₂O₅ (estimated as increase in total nitrogen or of P₂O₅ ofthe whole plant per day per 1 g. ‘residual dry weight’of the roots) appeared to undergo a similar but much smallerdiminution. It seemed probable, however, that in the presenceof MCPA a larger proportion of the carbohydrate actually formedwas utilized for synthesis of aminoacids and protein. In the plant as a whole there was no evidence of actual depletionof ‘available carbohydrate’ as a result of MCPAtreatment, this fraction showing a steady increase in all treatmentsthroughout the experiment. The rate of increase was, however,much reduced by MCPA treatment. The ‘tops’ presentedmuch the same picture as the whole plant, but for the rootsthe situation was quite different. While the roots of the ‘no-MCPA’plants and also of the ‘MCPA-water’ plants showeda steady increase in available carbohydrate, those of the ‘MCPA-nutrient’plants rose only very slightly (from the initial value of 8mg. per plant to about 10 mg.) during the first 2 days, andthen in the next 2 days declined to a value (about 6 mg.) belowthe initial and remained at this low level for the rest of theexperiment. It is suggested that the phytocidal effect of 2-methyl-4-chlorophenoxyaceticacid in the presence of nutrient may be due to depletion ofthe ‘available carbohydrate’ supplies in the roots,which is shown to be brought about, in part, by reduced transportfrom the tops, and partly by the relatively greater utilizationof the carbohydrate present. These results offer an explanationfor the facts that plants showing vigorous growth are more easilykilled by MCPA and that perennial plants, particularly thosewith storage tissues in their roots, are more resistant. Further,they suggest the useful practical application that MCPA treatmentshould be given when the carbohydrate reserves of the rootsare at a minimum. For perennial plants, conditions might beexpected to be optimal for the application of MCPA in late spring,at a time when the first ‘flush’ of growth is slowingdown and before any appreciable new reserves of carbohydratehave been accumulated. It was also shown that 2-methyl-4-chlorophenoxyacetic acid preventedthe net synthesis of starch, but still permitted an appreciablenet formation of sucrose. 2-methyl-4-chlorophenoxyacetic acid appeared to have no effecton the uptake of potassium, calcium, or of magnesium. The lackof effect on potassium is contrasted with the previous observationby Rhodes, Templeman, and Thruston (1950) that sub-lethal concentrationsof MCPA, applied over a relatively long period to the rootsof tomato plants, specifically depressed the uptake of potassium.     

Analysis of a Juvenile-like Condition Affecting Flowering in the Black Currant (Ribes nigrum)

Rooted shoots of the black currant with fewer than 20 nodes,taken from mature bushes, cannot be induced to initiate flowersby short-day treatment. This ‘juvenile’ conditionhas been shown to be unrelated to ‘size’ attributes,such as leaf area, but is associated with the proximity of theshoot tips to the roots. Aerial rooting on long ‘mature’shoots prevents flower initiation. Gibberellic acid applicationprevents flowering in mature shoots, as do high levels of IBA.Cytokinins have no effect. Abscisic acid and CCC applicationgave some promotion of flowering in long shoots in long-day,but did not overcome the ‘juvenility’ of short shoots.Gibberellin assay reveals activity in the roots and lower partsof stems, while none could be detected in the tops of long shoots.It is suggested that the correlation between shoot length andgibberellin activity may be decisive in determining juvenilityin the black currant and possibly other species.     

The Developmental Anatomy of the Root System in Yam Bean, Pachyrhizus erosus Urban

Investigations revealed that the anatomy of the primary radicularroot of yam bean (Pachyrhizus erosus L.) was typically dicotyledonousexcept that the xylem was not completely developed centripetally.Most of the roots had tetrarch xylem, although a few triarchand pentarch roots were also observed. In both tuberous andnon-tuberous roots, secondary thickening occurred by the formationof the meristematic vascular cambium which formed secondarytissues in a normal fashion. Subsequently, tuberization wasinitiated in the secondary xylem by the development of anomalous‘secondary’ cambia from parenchyma cells surroundingvessel elements. Anomalous ‘secondary’ cambia alsodeveloped from parenchyma cells not associated with vessels.Subsequently, anomalous ‘tertiary’ cambia differentiatedfrom tissues produced by the anomalous ‘secondary’cambia. Activities of these anomalous cambia resulted in theproduction of parenchyma storage cells and were chiefly responsiblefor the growth of the mature tuber. Pachyrhizus erosus L., yam bean, tuberous root, anatomy, anomalous ‘secondary’ cambia, anomalous ‘tertiary’ cambia, centripetal xylem development     

Effect of Source of Nitrogen on the Growth of Fiskeby Soya Bean: the Carbon Economy of Whole Plants

Fiskeby V soya bean was grown from seed germination to seedmaturation with two contrasting patterns of nitrogen metabolism:either wholly dependent on dinitrogen fixation, or with an abundantsupply of nitrate nitrogen, but lacking root nodules. The carbonand nitrogen economies of the plants were assessed at frequentintervals by measurements of photosynthesis, shoot and rootrespiration, and organic and inorganic nitrogen contents. Plantsfixing atmospheric nitrogen assimilated only 25–30 percent as much nitrogen as equivalent plants given nitrate nitrogen:c. 40 per cent of the nitrogen of ‘nitrate’ plantswas assimilated after dinitrogen fixation had ceased in ‘nodulated’plants. The rates of photosynthesis and respiration of the shootsof soya bean were not markedly affected by source of nitrogen;in contrast, the roots of ‘nodulated’ plants respiredtwice as rapidly during intense dinitrogen fixation as thoseof ‘nitrate’ plants. The magnitude of this respiratoryburden was calculated to increase the daily whole-plant respiratory loss of assimilate by 10–15 per cent over thatof plants receiving abundant nitrate. It is concluded that ‘nodulated’plants grew more slowly than ‘nitrate’ plants inthese experiments for at least two reasons: firstly, the symbioticassociation fixed insufficient nitrogen for optimum growth and,secondly, the assimila tion of the nitrogen which was fixedin the root nodules was more energy-demanding in terms of assimilatethan that of plants which assimilated nitrogen by reducing nitratein their leaves.     

Analysis of Shoot Apical Growth of Picea sitchensis Seedlings

During the first 100 days after sowing (March-June) the followingchanges took place at the terminal shoot apices of Picea sitchensisseedlings: plastochrones (T) decreased from over 24 h to 4 h;apical domes enlarged from less than 0·20 mm to 0·45mm diameter (D); the ‘projected’ area of tissuesproduced by the apical domes (i.e. viewed from above) increasedin amount from less than 0·012 to 0·024 mm² day^-1;about 15 per cent of this tissue was re-invested in the apicaldomes, the rest was used to produce primordia; and the volume-doublingtimes of the apical dome tissues decreased from over 150 h to50 h. After 100 days there was no further re-investment in theapical domes, but the domes did not decrease abruptly in size.Less tissue was produced per day, but the primordia were smallerso that the rate of primordia formation did not fall precipitously.Plastochrone ratios were inversely related to D, but the relationshipbetween T and D depended on whether T was decreasing or increasing.Progenies which were known to be fast growing tended to build-uptheir apical domes rapidly (i.e. have large ‘re-investmentratios’) and to be capable of producing small primordia.These attributes can evidently be evaluated on seedlings andcould help to lessen the cost of tree breeding progeny-testprogrammes. meristem, Picea sitchensis, Sitka spruce, growth, shoot apex     

Evaluating the 'Labeled Magnitude Scale' for Measuring Sensations of Taste and Smell

The Labeled Magnitude Scale (LMS) is a semantic scale of perceptualintensity characterized by a quasi-logarithmic spacing of itsverbal labels. The LMS had previously been shown to yield psychophysicalfunctions equivalent to magnitude estimation (ME) when gustatory,thermal and nociceptive stimuli were presented and rated together,and the upper bound of the LMS was defined as the ‘strongestimaginable oral sensation’. The present study comparedthe LMS to ME within the more limited contexts of taste andsmell. In Experiment 1, subjects used both methods to rate eithertaste intensity produced by sucrose and NaCl or odor intensityproduced by acetic acid and phenyl ethyl alcohol, with the upperbound of the LMS defined as either the ‘strongest imaginabletaste’ or the ‘strongest imaginable odor’.The LMS produced psychophysical functions equivalent to thoseproduced by ME. In Experiment 2 a new group of subjects usedboth methods to rate the intensity of three different tastequalities, with the upper bound of the LMS defined as the ‘strongestimaginable [sweetness, saltiness, or bitterness]’. Inall three cases the LMS produced steeper functions than didME. Experiment 3 tested the hypothesis that the LMS yields datacomparable to ME only when the perceptual domain under studyincludes painful sensations. This hypothesis was supported whenthe LMS again produced steeper functions than ME after subjectshad been explicitly instructed to omit painful sensations (e.g.the ‘burn’ of hot peppers) from the concept of ‘strongestimaginable taste’. We conclude that the LMS can be usedto scale sensations of taste and smell when they are broadlydefined, but that it should be modified for use in scaling specifictaste (and probably odor) qualities. The implications of theseresults for theoretical issues related to ME, category-ratioscales and the size of the perceptual range in different sensorymodalities are discussed. Chem. Senses 21: 323–334, 1996.     

The Initiation, Growth, and Emergence of Leaf Primordia in Fragaria

The leaf initiation rate in Fragaria vesca (var. ‘RoyalSovereign’) has been compared with the elongation rateof the leaf primordia at different seasons. Certain conceptionsof growth correlation within the bud are presented. Experimentson the nature of elongation and emergence of primordia are described,and the causes of emergence are discussed.     

The Extraction, Solubility, and Characterization of Two Groups of Barley Storage Polypeptides

This paper reports further studies on the characteristics ofthe storage protein fraction (hordein) of barley. Hordein consistsof two groups of polypeptides (termed ‘B’ and ‘C’)coded by two separate but linked loci. Whereas the ‘C’polypeptides are readily soluble and extracted in 60% (v/v)ethanol at room temperature, the ‘B’ group is moresoluble in, and therefore more efficiently extracted by, 50%(v/v) propan-1-ol or 45% (v/v) propan-2-ol at elevated temperaturesand in the presence of 2-mercaptoethanol. However, the mostefficient conditions for hordein extraction (50% propan-1-ol+ 2% (v/v) 2-mercaptoethanol at 60 °C) also extract somecontaminating non-hordein polypeptides resulting in an apparentlyincreased lysine content of the hordein fraction. Amino acid analysis of the purified ‘B’ and ‘C’hordein groups shows that, whereas ‘C’ hordein containsmore glutamate + glutamine, proline, and phenylalanine than‘B’ hordein, it contains only traces of lysine andsulphur amino acids in contrast to ‘B’ hordein whichcontains 0·5% lysine 0·6% methionine, and 2·5%cysteine. Equilibrium sedimentation analyses carried out on the purified‘B’ and ‘C’ groups indicates that thepreparations were reasonably monodisperse with molecular weightsof approximately 32 000 and 52 000 respectively. These valuesare considerably lower than those previously determined by SDS-PAGE.     

Experimental and Analytical Studies of Pteridophytes: XXXVII. A Note on the Inception of Microphylls and Macrophylls

In an attempt to shed new light on the nature of microphyllsand macrophylls, a study has been made of leaf inception inselected materials, including Psilotum, Tmesipteris and otherpteridophytes, and flowering plants such as Cuscuta with greatly‘reduced’ leaves. It is shown that the incipientprimordia of the small scale-like leaves of Psilotum and ofthe quite substantial, though microphyllous, laminate leavesof Tmesipteris are closely comparable and that there are noessential differences in the histological organization of incipientmicrophylls and incipient macrophylls. In parasitic speciessuch as Cuscuta, with small scale-like leaves, the organizationof the apical meristem and the inception of primordia are asin normal autotrophic species. The so-called ‘reduced’leaves and the microphyllous condition of some pteridophytesare attributable to a physiological-genetical limitation ofgrowth of primordia in the subapical regions of the shoot. Theconclusions which may be drawn from these observations are discussed.     

Studies in the Regeneration of Horseradish: II. Correlation Phenomena

Regeneration has been studied in fragments of various sizes,and complete plants, together with the effect of externally-appliedß-indolylacetic acid (I.A.A.). The main conclusionsare as follows: (1) In the intact plant regeneration is inhibited by the growingcrown; in cuttings, I.A.A. will reduce the rate of primordium-formation,but cannot entirely suppress it. (2) The bud/root ratio among differentiated primordia is about0·5–0·9 in long cuttings; it rises sharplyin cuttings less than 2 cm. long, and falls in the presenceof I.A.A. Most, though probably not all, of the observationsconcerning this ratio can be explained on a simple auxin-levelhypothesis. (3) I.A.A., at an appropriate concentration, depresses the extensionof buds and promotes that of roots. On each cutting, only one(proximal) bud will normally extend—but this form of dominancecannot be exactly simulated by I.A.A., and more than one hormoneseems to be involved. The results are discussed from the point of view of hormonetheories of regeneration, and it is concluded that direct measurementsof internal auxin-content will be essential before the phenomenacan be interpreted with consistency.     

Regeneration of Tissues in Wounded Stems: A Quantitative Study

When a dicotyledonous stem is wounded by longitudinally splittinga young internode into halves, cells near the cut surface proliferateto form a callus within which vascular tissues differentiateand tend to restore a vascular cylinder in each half. Threephases of regeneration after wounding were identified and quantifiedin stems of three Solanaceous species. (1) In an initial ‘lag’phase, lasting about 2 d, neither cell division nor enlargementwere detected, but mitotic figures were observed within about300 µm of the cut surface. (2) Throughout a second, ‘division’phase, from about days 2–10, cell division and enlargementoccurred. Both were initiated mainly in the two cell layersnearest the surface. A mass of callus formed, with new cellwalls mostly parallel to the surface. Cell enlargement laggedbehind cell division for the first few days, so that mean radialcell diameter decreased until day 6, thereafter remaining almostconstant at 30–40 µm. Towards the end of this phase,mitoses ceased within the callus except in the positions ofthe future vascular and cork cambia, where radial cell diameterfell towards a constant 15–20 µm. (3) During a third,‘differentiation’ phase, cell division was restrictedto the cambial zones, and derivatives differentiated into cork,phloem or xylem according to position. The rate of increasein cell number per transect was 1.5–2.0 cells d^–1,of which more than half was xylem. Capsicum annuum L., sweet pepper, Lycopersicon esculentum Mill., tomato, cambium, cell division, differentiation, regeneration, wounding of stems, xylem     

Enzymic Maceration of Citrus Callus and the Regeneration of Plants from Single Cells

The maceration medium comprised a basal nutrient medium (BM)containing an optimum concentration of 3% (w/v) sucrose. Mannitoland sorbitol were inferior osmotica. Addition of potassium dextransulphate adversely affected maceration. ‘Macerozyme’was not as effective as ‘Macerase’ in the productionof single cells. The optimal concentration of ‘Macerase’was found to be 2–3% (w/v). Single cells obtained by filtering the macerate were rinsedwith BM and cultured in, and on, agar media comprising: BM;BM + 500 mg 1^–1 malt extract (ME); and BM + 10% (v/v)coconut milk (CM). No growth or organization was observed incultures where cells were mixed in with warm medium prior togelling. When spread on the surface of gelled media supplementedwith ME and CM, proliferation and organization occurred. Manymicroscopic globular proembryoids developed within 3 weeks onthe supplemented media. Microscopic torpedo-shaped embryoidswere frequently observed on BM + CM, rarely on BM + ME, andnot at all on unsupplemented BM. The high frequency of microscopic globular proembryoids, andlater of macroscopic pseudo-bulbils, formed on BM + ME leadsus to postulate that pseudobulbils are derived from globularproembryoids in which polarity is not established by the 16to 32-cell stage. Microscopic torpedo-shaped embryoids probablygive rise to macroscopic heart-shaped embryoids which developinto plantlets. The technique reported in this article provides an ideal systemfor examining embryogenesis per se and for studying the effectsof various treatments on embryogenesis and organ differentiationin vitro. It also affords excellent opportunities for the breedingof solid mutant plants.     

IAA Amino Acid Conjugates Induce Differentiation of Tracheary Strands in Lettuce Pith Explants

Each of four amino acid conjugates of IAA was able to replacethe IAA requirement for xylogenesis in lettuce pith explants,when supplied at concentrations ten to 100 times those optimalfor IAA. Tracheary development induced by these conjugates tendedto be slightly slower and less in amount than with IAA, andthe tracheary strands shorter and less regular. Responses differedsomewhat among the four conjugates: IAA-D, L-aspartate gavedevelopment most like that with free IAA, and IAA-D, L-phenylalanineoften yielded the weakest tracheary development, while responsesto IAA-L-alanine and IAA-glycine were intermediate. The resultsare interpreted in terms of the ‘bound’ IAA conjugatesdiffusing into the pith explants and becoming xylogenic onlyon hydrolysis to ‘free’ IAA. As tracheary strandformation is believed to result from IAA fluxes, it seems thatthe free IAA also moved through the discs, presumably towardsthe surfaces where it degrades rapidly. Tracheary strand formationin these explants can be compared with vascular strand formationin the normal shoot tip, where IAA conjugates (auxin ‘precursors’)move acropetally and are hydrolysed to free IAA especially inthe young leaf primordia, we suggest, yielding local sourcesof IAA which may contribute both to the phyllotactic spacingof primordia and, moving basipetally, to the definition of theauxin pathways that develop as procambial strands behind individualleaf primordia. Lactuca sativa, lettuce, IAA conjugates, tracheary element differentiation, pith explants, xylem strands     

Effect of Temperature on the Radial Exchange of Labelled Water in Maize Roots

The temperature dependence of the efflux kinetics of labelledwater in isolated maize roots has been studied. The purposeof these experiments was to obtain the energy of activation,E (kcal/mole), of the rate-limiting step in this radial exchangeprocess under various experimental conditions. Estimates ofE were obtained from linear relations between ln{D'_w} and thereciprocal of the absolute temperature; values of the apparentdiffusion coefficient, D'_w, of labelled water in the root werefound from an analytical treatment of the efflux data in termsof a cylindrical diffusion model. The energy of activation forlabelled-water exchange in normal roots was 14.9 kcal/mole.The corresponding value for ‘dead’ (boiled) rootswas 3.9 kcal/mole. These values of E substantiate the view thatin normal roots the penetration of water across the membranesof the root cells constitutes the rate-determining step in theefflux whereas in ‘dead’ roots extracellular diffusionof water is the source of rate-control. Similar temperature dependence studies were performed on theefflux kinetics from normal and ‘dead’ roots treatedwith 10^–5 M phenylmercuric acetate (PMA). The energiesof activation for labelled-water exchange in normal and ‘dead’roots under these conditions were respectively 15.5 and 5.3kcal/mole. Moreover, the results of the efflux experiments onPMA-treated roots were considered to indicate that this inhibitorproduces an alteration in some structural aspect of the rate-controlling‘membranes’.     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the‘whorl; and the remainder of the shoot, where they werewidely spaced, the ‘interwhorl’ stem. In spring,the terminal bud started expanding before the ‘whorl’buds which preceded the ‘interwhorl’ stem buds;completion of the flush of growth, determined by the end ofleaf expansion, occurred in the reverse order, ‘interwhorl’> ‘whorl’ > terminal. Similarly bud expansionstarted at the top of the crown and progressed downwards, andthe first shoots to complete their flush were at the bottomof the crown. Approximately 60% of the buds on each shoot beganexpanding in spring but only about half of these formed branches.Bud abscission began in May and by Sep. 45% of buds originallypresent had abscised. Most of-the buds that did not abscisewere the small buds at the base of the shoot that were not originallyassociated with a leaf. Approximately 42% of ‘whorl’buds and 28% of MnterwhorP stem buds formed branches. ‘Whorl’branches were approx. 60% longer that ‘interwhorl’stem branches; buds on the lower surface of the shoot producedlonger branches than those on the upper surface. The implicationsof the results for the development of crown form and selectionof superior oak are discussed. Quercus petraea, oak, buds, branches, crown form     

Factors Affecting the Abscission of Reproductive Organs in Yellow Lupins (Lupinus luteus L.): III. ENDOGENOUS GROWTH SUBSTANCES IN VIRUS-INFECTED AND HEALTHY PLANTS AND THEIR EFFECT ON ABSCISSION

Extracts of small and mature-size lupin pods yielded four substancesaffecting the growth of wheat-coleoptile sections: one acidpromotor (A), two acid inhibitors(B and X), and one neutralinhibitor(Y). Inhibitor B was extremely active, however, coleoptile sectionsshowed no signs of toxic effects; they resumed growth at a rapidrate after rinsing them and adding ß-indolylaceticand (IAA) to the medium. 1 µg of IAA was required to counteractthe effect of ‘B’ extracted from 230 mg. Of tissue.On an equal fresh weight basis the inhibiting action of ‘B’in lupin pods was 500–1,500 times more potent than thatof ‘inhibitor ß’ in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded3 times the amount of ‘A’ of healthy plants (equivalentto 1 µg. IAA 0.3 µg. IAA per 25 g. of tissue respectively),and approximately the amount of ‘B’. Mature podsof virus-infected plants again yielded more‘A’,but also 2? times more ‘B’ than pods of healthyplants. Healthy pods yielded more ‘A’ than virus-infectedpods, and there was no difference in ‘X’. A lupin abscission test was developed and the effects of proximaland distal application of -naphthyl acetic acid (NAA) are presented,and discussed with respect to results of other abscission tests. ‘A’ accelerated abscission when applied proximally,and delayed or prevented it when applied distally. ‘B’strongly accelerated abscission when applied in either way.A possible mechanism explaining the abscission-inducing effectof developing pods on later flowers is discussed in terms ofthe substances ‘A’ and ‘B’. The partlyprevented abscission observed on virus-infected plants was foundto agree well with the proposed mechanism.     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the'whorl; and the remainder of the shoot, where they were widelyspaced, the ‘interwhorl’ stem. In spring, the terminalbud started expanding before the ’whorl’ buds whichpreceded the ‘interwhorl’ stem buds; completionof the flush of growth, determined by the end of leaf expansion,occurred in the reverse order, ‘interwhorl’     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.): 3. Partition of Assimilates between Root and Shoot during the Transition from Vegetative to Reproductive Growth

The partition of ¹⁴C labelled current assimilates to root insimulated swards of Lolium perenne cv. S24 was measured duringthe transition from vegetative growth in autumn to reproductivegrowth in spring under close to natural conditions of lightand temperature. Assimilate partitioning was also measured in‘established’ swards cut three times during thegrowing season and in vegetative ‘seedling’ swardsgrowing in autumn and in spring. All measurements were madewhen the swards had achieved more than 90 per cent light interception,and all swards were abundantly supplied with water and mineralnutrients. During autumn there was a gradual decrease in the proportionof assimilates partitioned to the roots in both the ‘established’and the ‘seedling’ swards. In the established swards,partition to roots was low over winter, increased during earlyspring, but decreased dramatically, later in the spring, whenstem elongation began. In contrast, in the unvernalized vegatativeseedling swards in spring, partition to roots remained high. The seasonal pattern of assimilate partitioning is consideredin relation to changes in the natural environment and the rateat which the crop fixed carbon in photosynthesis. A decreasein the proportion of assimilates partitioned to roots duringlate spring was significant in increasing the production ofshoot at that time but seasonal differences in partition contributedvery little to the marked differences in shoot growth betweenthe spring and autumn crop. Lolium perenne L., perennial ryegrass, partition of assimilates, flowering     

The Growth and Carbon Allocation Patterns of White Clover (Trifolium repens L.) Plants of Contrasting Branching Structure

The growth, morphology and carbon allocation patterns of F1progeny white clover (Trifolium repens L.) plants selected foreither low (‘LBF’) or high (‘HBF’) frequencyof stolon branching were compared in two controlled-environmentexperiments. Selections from within both a small-leaved (‘GrasslandsTahora’) and a large-leaved (‘Grasslands Kopu’)clover cultivar were compared, and plants were grown under arelatively lenient defoliation treatment (expt 1) or under threelevels of defoliation seventy (expt 2). Carbon allocation patternswere measured by ¹⁴CO₂ pulse-chase labelling using fully unfoldedleaves on the main (parent) stolon. LBF and HBF displayed consistent differences in the selectedcharacter though, within cultivars, the difference between selectionswas most pronounced for Kopu. The selections developed fundamentallydifferent branching structures resulting from differences inbranching frequency, with total branch weight per plant averaging122 mg for LBF and 399 mg for HBF (mean of both experiments).More C moved from parent stolon leaves to branches in HBF thanin LBF (mean 22.6% vs. 15.1% respectively of the ¹⁴C exportedfrom source leaves). More C also moved to stolon tissue in HBF,but, counterbalancing this and the difference in allocationto branches, less moved to developing leaves and roots on theparent stolon itself compared to LBF. However, the total weightof developing leaves and roots per parent stolon was generallygreater in HBF than in LBF, probably reflecting greater C importby these sinks from the higher number of branches present perplant in the former selection. HBF plants were consistentlylarger at harvest than LBF plants. There were no defoliationtreatment x selection interactions in C allocation patternsin expt 2. The implications of the results for plant performancein grazed pastures are discussed. Branching, carbon translocation, defoliation, growth, morphology, Trifolium repens, white clover